Machine tank for electric discharge machine

ABSTRACT

A work tank ( 20 ) for an electric discharge machine includes a tank wall ( 21 ) having an opening in a front surface and surrounding a workpiece; a front door ( 31 ) horizontally movable between an unlock position, where the front door is vertically movable, and a lock position, where the opening is closed in a generally liquid-tight relationship; a pair of brackets ( 32 ) attached to both sides of the front door and extending rearwardly; a handle lever ( 51 ) capable of pivoting about a fulcrum ( 35 ) and supported on at least one of the brackets; and a cam follower, fixed to the handle lever further forward than the pivot, the cam follower being vertically movable between a first position (H 1 ) higher than the fulcrum and a second position (H 2 ) lower than the fulcrum. The cam follower is fitted loosely into a groove ( 62 ) extending vertically and formed in a rail block ( 61 ). Horizontal movement of the cam follower is restricted. When the cam follower is at the first position, the front door is in the unlock position and is vertically movable. When the cam follower is at the second position, the front door is in the lock position and is held closed within the opening in a generally liquid-tight relationship.

FIELD OF THE INVENTION

The present invention relates to an electric discharge machine forgenerating electric discharges in a working gap formed between a toolelectrode and a workpiece while supplying dielectric fluid to theworking gap. More particularly, the present invention relates to a worktank for storing dielectric fluid in which a workpiece has beenimmersed, or gathering dielectric fluid which, after being jetted at theworking gap, is scattered away.

DESCRIPTION OF THE RELATED ART

Generally, a workpiece is positioned inside a work tank, and the worktank is filled with dielectric fluid such as kerosene or water with highelectrical resistivity. A tool electrode is positioned extremely closeto the workpiece. When a power pulse is applied across the workpiece andthe tool electrode, the insulation characteristics of the dielectricfluid in the work gap are broken down and an electric discharge isproduced. Microscopic amounts of the workpiece material are evaporatedor molten by the heat caused by this electric discharge, and washed intothe dielectric fluid. In order to restore the insulation characteristicsof the dielectric in the working gap, application of the power pulse isstopped for a fixed time. During electric discharge machining, thebreakdown and restoration of the insulation characteristics of thedielectric fluid is repeated cyclically. In addition to its function asan insulator, the dielectric fluid also functions to wash away scraps ofthe workpiece material, and to cool the working gap. Electric dischargemachining methods have been used in which dielectric fluid is jettedinto the work gap using an appropriate nozzle without storing thedielectric fluid in a work tank. With this type of electric dischargemachining method, in order to save dielectric fluid, a work tankenclosing the workpiece is used to catch and gather any dielectric fluidwhich scatters from the working gap.

At least the front part of the work tank is movable so that inpreparation for machining an operator can easily get close to theworkpiece or tool electrode inside the work tank. For example, a worktank having a front door which is hinged on one side and can turnhorizontally, is known. This type of work tank requires a large spacewhen opening the front door. Japanese Laid-open Patent 8-71850 disclosesa work tank having a front door capable of being folded in half from topto bottom. The work tank disclosed in this publication makes the spacerequired to open the front door smaller.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a work tank for anelectric discharge machine that can rapidly perform continuous closingand locking of a front door.

Another object of the present invention is to provide a work tank for anelectric discharge machine that can rapidly perform continuous unlockingand opening of a front door.

Yet another object of the present invention is to provide a work tankfor an electric discharge machine that does not require a large spacewhen opening a front door.

According to the present invention, a work tank for an electricdischarge machine in which dielectric fluid is supplied between aworkpiece and a tool electrode comprises

a tank wall having an opening on a front side and surrounding aworkpiece,

a front door horizontally movable between an unlock position where thefront door is vertically movable, and a lock position where the openingis closed in a generally liquid-tight relationship,

a pair of brackets attached to both sides of the front door andextending rearward,

a handle lever supported on at least one of the pair of brackets so asto pivot about the fulcrum,

a cam follower, fixed to the handle lever further forward than thefulcrum, and being vertically movable between a first position higher upthan the fulcrum and a second position lower down than the fulcrum, and

a movement restricting member for restricting horizontal movement of thecam follower.

When the cam follower is at the first position, the front door is in theunlock position and is vertically movable. When the cam follower is atthe second position, the front door is in the lock position and theopening is held closed in generally liquid-tight relationship.

Preferably, the handle levers are supported on each of the pair ofbrackets, and a handle is provided for connecting respective tips of thehandle levers.

The movement restriction member is preferably a rail block having avertically extending groove into which the cam follower is looselyfitted.

Preferably, a guide block, having a guide groove extending verticallyand then extending rearward from the upper end, is attached to the tankwall, and a guide pin that can be fitted into the guide groove isprovided on the bracket.

It is also preferable to provide stopper pins on the bracket, forrestricting the pivoting angle of the handle lever by contacting thehandle lever.

Other objects and novel features of the present invention will becomeclear upon reference to the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation illustrating an electric discharge machineadopting the work tank of the present invention.

FIG. 2 is a front elevation partially illustrating the work tank of FIG.1.

FIG. 3 is a side elevation partially illustrating the work tank of FIG.1, when the front door is positioned at the lower limit.

FIG. 4 is a cross sectional drawing partially illustrating the work tankof FIG. 1, viewed along line A—A in FIG. 3.

FIG. 5 is a side elevation partially illustrating the work tank of FIG.1, when the front door is not locked at the upper limit 5 position.

FIG. 6 is a side elevation partially illustrating the work tank of FIG.1, when the front door is locked at the upper limit position.

FIG. 7 is a drawing showing an operation of locking the front door ofthe work tank of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A work tank for an electric discharge machine, of the present invention,will now be described with reference to FIG. 1, FIG. 2, FIG. 3, FIG. 4,FIG. 5, FIG. 6 and FIG. 7.

As shown in FIG. 1, a work tank 20 of the present invention is mountedon a bed 12, and a workpiece (not shown in the drawing) is fixed to atable (not shown) provided at the bottom of the work tank 20. A head 13is attached to a front surface of a column 12 so as to move vertically,and an electrode holder 14 is attached to a lower end of the head 13.The work tank 20 includes generally four-sided tank wall 21 enclosingthe workpiece, and as shown in FIG. 2 an opening 22 is formed in thefront wall 21 a. Using the opening 22, an operator can easily get closeto the workpiece or tool electrode inside the work tank 20. A front door31 is provided in order to close the opening 22 in a generallyliquid-tight relationship. Elastic packing is attached to the front wall21 a along the edge of the opening 22. The packing prevents leakage ofdielectric fluid from a gap between the front wall 21 a and the frontdoor 31 when the door 31 is closed. The packing may be attached to thefront door 31. As shown in FIG. 3, brackets 32 are attached to both endsof the front door 31, and extend rearward, generally parallel to theside wall 21 b. In order to make it easy to replace the elastic packing,the brackets 32 may be detachable from the front door 31. Upper guidepins 33 and lower guide pins 34 are embedded in the brackets 32. Guideblocks 41, preferably made from engineering plastic having excellentabrasion resistance and low friction resistance, are attached to theside wall 21 b. Guide grooves 43 and 44, into which the upper and lowerguide pins 33 and 34 can be respectively fitted, are formed in the guideblocks 41. The upper and lower guide grooves 43 and 44 extend generallyvertically, and then extend generally horizontally rearward from theirupper ends. If the brackets 32, guided in the vertical part of the guidegrooves 43 and 44, are moved vertically from the lower limit positionshown in FIG. 3 to the upper limit position shown in FIG. 5, the frontdoor 31 closes the opening 22 in the front wall 21 a. Also, if thebrackets 32, guided in the horizontal part of the guide grooves 43 and44, are moved vertically from the position shown in FIG. 5 to theposition shown in FIG. 6, the front door 31 closes the opening 22 in agenerally liquid-tight relationship.

End stoppers 49 for determining the lower limit position of the brackets32 are provided, preferably close to the lower end of the guide blocks41. Fulcrum pins 35, extending generally parallel to the front wall 31,are attached to respective rear parts of the brackets 32. Handle levers51 are supported on the respective brackets 32 so as to pivot about thefulcrum pins 35. A handle 53 is connected to respective tip ends of thehandle levers 51. The handle 53 is positioned further forward than thefront door 31. An operator may move the front door 31 using this handle53. Stopper pins 36 and 37 for restricting the pivot angle of the handlelevers 51 are embedded in the brackets 32, further forward than thefulcrum pins 35.

As best seen in FIG. 3 and FIG. 5, when the handle levers 51 are incontact with the upper stopper pins 36, a line extending generallyupwards from the fulcrum pins 35 to the handle 53 slopes up at about 27degrees with respect to the horizontal.

As shown in FIG. 6, when the handle levers 51 are in contact with thelower stopper pins 37, a line extending generally downwards from thefulcrum pin 35 to the handle 53 slopes down at 27 degrees with respectto the horizontal. Lower ends of the rear sections of the brackets 32are bent, and form respective engagement sections 38.

As best seen in FIG. 5, when the front door 31 is at the upper limitposition, the engagement sections 38 are brought into contact withcontact members 92 attached to the side wall 21 b. The engagementsections 38 and the contact members 92 prevent the front door 31 fallingforward. Cam followers 52 are attached to the handle levers 51 betweenthe fulcrum pins 35 and the handle 53. Rail blocks 61 having avertically extending groove 62 formed therein are attached to the sidewall 21 b closely behind the guide blocks 41.

As best seen in FIG. 4, one end of each cam follower 52 is fixed to thehandle lever 51, and the other end is loosely fitted into the groove 62.A roller is preferably provided on the other end of the cam follower 52,so that the cam follower 52 can slide smoothly on the side surface ofthe groove 62. The difference between the width of the groove 62 and thediameter of the roller is much smaller than the length of the horizontalpart of the guide grooves 43 and 44. Accordingly, when the front door 31is moved horizontally, horizontal movement of the cam follower 52 isrestricted. Cut away slots 38 through which the cam followers 52 passare formed in the brackets 32.

Timing belts 71 are provided for synchronizing movement of the brackets32 provided on both sides of the work tank 20. The timing belts 71engage with upper and lower pulleys 72 and 73. The upper pulleys 72 areattached to respective pulley shafts 74 via bearings 73. The pulleyshafts 74 are fixed to the tank wall 21 close to upper ends of the railblocks 61. The lower pulleys 73 are attached to both ends of a pulleyshaft 75 extending along the front wall 21 a, and rotate in synchronism.The pulley shaft 75 is rotatably supported by bearings 77 contained inhousings 78. The housings 78 are attached to the tank wall 21 close toupper ends of the rail blocks 61. The timing belts 71 are linked to thebrackets 32 by link members 94 and press members 95. Since the twobrackets 32 thus move in synchronism, the guide pins 33 and 34 will notget stuck in the guide grooves 43 and 44.

Torsion coil springs 81 are wound around the pulley shaft 75. In orderto generate a force acting to reduce the weight of the front door 31 onthe timing belts 71, one end of the torsion coil springs 81 may be fixedto the pulley shaft 75 using metal fittings 82. Additionally, the forcerequired to operate the front door 31 is reduced by the torsion coilsprings 81. In order to provide a predetermined force and to move thebrackets 32 in synchronism, a chain or a wire may be used in lieu of thetiming belt 71.

The opening and closing of the front door 31, and a locking operation,will now be described.

FIG. 3 and FIG. 4 show the front door 31 being open at the lower limitposition. At this time, the handle levers 51 come into contact with theupper stopper pins 36, and the brackets 32 come into contact with theend stoppers 49. In order to close the front door 31, the operator gripsthe handle 53 and lifts the handle 53 upwards. FIG. 5 shows the frontdoor 31 lifted up to the upper limit position. Next, the operator pushesthe handle 53 so as to cause the guide pins 33 and 34 to move along thehorizontal part of guide grooves 43 and 44. Thereafter, the handle 53 ispushed down. As shown in FIG. 6, the handle levers 51 rotate in acounterclockwise direction and come into contact with the lower stopperpins 37. The time required to move the front door 31 from the lowerlimit position to the upper limit position and then move from an unlockposition to a lock position is about 2 or 3 seconds. In this way, theclosing and locking operation of the front door 31 is carried outcontinuously in a short time with operation of a single handle. Sincethe movement from the position shown in FIG. 5 to the position shown inFIG. 6 is horizontal, there is an advantage that the packing attached tothe front door 31 is unlikely to be damaged.

FIG. 7 schematically shows the respective positions of the handle 53,cam followers 52 and fulcrum pins 35 when the front door 31 is movedbetween the unlock position and the lock position. The cam followers 52only move in the vertical direction because of the rail block 61. Whenthe front door 31 is in the unlock position, the cam followers 52 arepositioned at a point H1 higher than the fulcrum pins 35. At this timethe fulcrum pins 35 are positioned at point P1 in the horizontaldirection. If the operator pushes the handle 53 down, the cam followers52 move downwards and the fulcrum pins 35 move horizontally backwards.When the cam followers 52 are positioned at the point HO and the camfollowers 52 and the fulcrum pins 35 are arranged horizontally levelwith each other, the fulcrum pins 35 are positioned at point P0 which isas far to the rear as they can go. At this time an elastic force of thepacking pushing the front door 31 forwards is at a maximum. If theoperator pushes the handle 53 further down, and the cam followers 52 arepositioned at point H2, lower than point H0, the fulcrum pins 35 arepositioned at point P2. At this time, the front door 31 is positionedbackwards from the unlock position by a distance L between the point P1and the point P2. As the point P2 is positioned further forward than thepoint P0, the cam followers 52 do not return naturally from point P2 topoint P0. If the operator pulls the handle 53 forwards and up and thehandle levers 51 come into contact with the guide pins 36, the frontdoor 31 is unlocked. Following the unlocking operation, if the operatorlowers the front door 31 from the upper limit position to the lowerlimit position, the front door 31 is opened. In this way, according tothe present invention, the opening and unlocking operations of the frontdoor 31 are carried out continuously by simply operating the handle 53.

The illustrated embodiment has been selected simply to describe the gistand practical application of the present invention. The scope of thepresent invention is defined by the appended claims.

What is claimed is:
 1. A work tank for an electric discharge machine forproviding dielectric fluid between a workpiece and a tool electrode,comprising: a work tank for surrounding the workpiece, said work tankincluding a tank wall having an opening on a front side thereof; a frontdoor movable in a generally horizontal direction between an unlockposition where the front door is vertically movable, and a lock positionwhere the opening is closed in a generally liquid-tight relationship; apair of brackets, each attached to a respective side of the front door,and extending rearwardly thereof; a pair of fulcrums, each attached to arespective bracket; a pair of handle levers, each supported on arespective bracket so as to pivot about the respective fulcrum; a handlefor connecting respective tips of the handle levers; a cam follower,fixed to the handle lever forward of the fulcrum, and vertically movablebetween a first position higher than the fulcrum, and a second positionlower down than the fulcrum; and a movement restricting member forrestricting horizontal movement of the cam follower.
 2. A work tank foran electric discharge machine for providing dielectric fluid between aworkpiece and a tool electrode, comprising: a work tank for surroundingthe workpiece, said work tank including a tank wall having an opening ona front side thereof; a front door movable in a generally horizontaldirection between an unlock position where the front door is verticallymovable, and a lock position where the opening is closed in a generallyliquid-tight relationship; a pair of brackets, each attached to arespective side of the front door, and extending rearwardly thereof; afulcrum, and a handle lever supported on at least one of the pair ofbrackets so as to pivot about the fulcrum; a cam follower, fixed to thehandle lever forward of the fulcrum, and vertically movable between afirst position higher than the fulcrum, and a second position lower downthan the fulcrum; and a movement restricting member for restrictinghorizontal movement of the cam follower.
 3. The work tank of an electricdischarge machine according to claim 2, wherein the movement restrictingmember includes a rail block having a generally vertically extending forloosely fitting the cam follower.
 4. The work tank of an electricdischarge machine according to claim 3, wherein the rail block isattached to the tank wall.
 5. The work tank of an electric dischargemachine according to claim 2, further comprising a guide block, saidguide block having a guide groove extending generally vertically andthen extending generally horizontally rearward from an upper endthereof, and a guide pin provided on the bracket so as to be fitted intothe guide groove.
 6. The work tank of an electric discharge machineaccording to claim 5, wherein the guide block is attached to the tankwall.
 7. The work tank of an electric discharge machine according toclaim 2, further comprising stopper pins, said stopper pins beingprovided on the bracket so as to come into contact with the handle leverfor restricting the pivot angle of the handle lever.
 8. The work tank ofan electric discharge machine according to claim 2, further comprising apacking attached to at least one of the tank wall and the front door forpreventing leakage of dielectric fluid between the tank wall and thefront door.
 9. The work tank of an electric discharge machine accordingto claim 2, further comprising a pair of timing members respectivelyconnected to the pair of brackets for synchronizing movement of the pairof brackets.
 10. The work tank of an electric discharge machineaccording to claim 2, further comprising a pulley shaft, and lowerpulleys fixed to the ends of the pulley shaft for respectively engagingwith the pair of timing members, and upper pulleys fixed to the tankwall.
 11. The work tank of an electric discharge machine according toclaim 10, further comprising coil springs, said coil springs having oneend fixed to the pulley shaft for generating a force for reducing theweight of the front door the respective timing members.
 12. The worktank of an electric discharge machine according to claim 9, furthercomprising force generating means for generating a force for reducingthe weight of the front door an the timing members.